首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5145篇
  免费   527篇
  国内免费   15篇
耳鼻咽喉   13篇
儿科学   198篇
妇产科学   90篇
基础医学   756篇
口腔科学   134篇
临床医学   461篇
内科学   857篇
皮肤病学   62篇
神经病学   385篇
特种医学   325篇
外科学   848篇
综合类   162篇
一般理论   31篇
预防医学   382篇
眼科学   92篇
药学   533篇
中国医学   10篇
肿瘤学   348篇
  2022年   34篇
  2021年   78篇
  2020年   46篇
  2019年   73篇
  2018年   92篇
  2017年   53篇
  2016年   80篇
  2015年   95篇
  2014年   125篇
  2013年   192篇
  2012年   231篇
  2011年   218篇
  2010年   164篇
  2009年   152篇
  2008年   189篇
  2007年   201篇
  2006年   238篇
  2005年   219篇
  2004年   214篇
  2003年   188篇
  2002年   183篇
  2001年   190篇
  2000年   196篇
  1999年   170篇
  1998年   100篇
  1997年   101篇
  1996年   90篇
  1995年   84篇
  1994年   76篇
  1993年   79篇
  1992年   126篇
  1991年   118篇
  1990年   101篇
  1989年   95篇
  1988年   107篇
  1987年   75篇
  1986年   78篇
  1985年   75篇
  1984年   51篇
  1983年   52篇
  1982年   38篇
  1981年   33篇
  1980年   38篇
  1979年   58篇
  1978年   44篇
  1977年   52篇
  1976年   47篇
  1975年   36篇
  1974年   32篇
  1973年   43篇
排序方式: 共有5687条查询结果,搜索用时 15 毫秒
51.
Expression of luminal and basal cytokeratins in human breast carcinoma   总被引:32,自引:0,他引:32  
We have examined basal and luminal cell cytokeratin expression in 1944 cases of invasive breast carcinoma, using tissue microarray (TMA) technology, to determine the frequency of expression of each cytokeratin subtype, their relationships and prognostic relevance, if any. Expression was determined by immunocytochemistry staining using antibodies to the luminal cytokeratins (CKs) 7/8, 18 and 19 and the basal markers CK 5/6 and CK 14. Additionally, assessment of alpha-smooth muscle actin (SMA) and oestrogen receptor status (ER) was performed. The vast majority of the cases showed positivity for CK 7/8, 18 and 19 indicating a differentiated glandular phenotype, a finding associated with good prognosis, ER positivity and older patient age. In contrast, basal marker expression was significantly related to poor prognosis, ER negativity and younger patient age. Multivariate analysis showed that CK 5/6 was an independent indicator for relapse free interval. We were able to subgroup the cases into four distinct phenotype categories (pure luminal, mixed luminal/basal, pure basal and null), which had significant differences in relation to the biological features and the clinical course of the disease. Tumours classified as expressing a basal phenotype (the combined luminal plus basal and the pure basal) were in a poor prognostic subgroup, typically ER negative in most cases. These findings provide further evidence that breast cancer has distinct differentiation subclasses that have both biological and clinical relevance.  相似文献   
52.
53.
Degenerate PCR primers derived from conserved regions of the eubacterial groESL heat shock operon were used to amplify groESL sequences of Ehrlichia equi, Ehrlichia phagocytophila, the agent of human granulocytic ehrlichiosis (HGE), Ehrlichia canis, Bartonella henselae, and Rickettsia rickettsii. The groESL nucleotide sequences were less conserved than the previously determined 16S rRNA gene sequences of these bacteria. A phylogenetic tree derived from deduced GroEL amino acid sequences was similar to trees based on 16S rRNA gene sequences. Nucleotide sequences obtained from clinical samples containing E. equi, E. phagocytophila, or the HGE agent were very similar (99.9 to 99.0% identity), and the deduced amino acid sequences were identical. Some divergence was evident between nucleotide sequences amplified from samples originating from the United States (E. equi and the HGE agent) and sequences from the European species, E. phagocytophila. A single pair of PCR primers derived from these sequences was used to detect E. chaffeensis and HGE agent DNA in blood samples from human patients with ehrlichiosis.  相似文献   
54.
Seventy-eight aerotolerant Campylobacter isolates were characterized phenotypically and by DNA hybridization (hydroxyapatite method at 50 and 65 degrees C). Two DNA relatedness groups were found. (i) Sixty-four strains belonged to aerotolerant Campylobacter DNA hybridization group 2. These organisms were isolated from humans, primarily with diarrheal illness, and animals on several continents. Strains were aerotolerant at 30 and 36 degrees C and catalase negative or weakly catalase positive, grew in media containing glycine and on MacConkey agar, were susceptible to nalidixic acid, and were resistant to cephalothin. The name Campylobacter butzleri sp. nov. is proposed for this group. (ii) DNA hybridization group 1 consisted of the type strain of Campylobacter cryaerophila and 13 additional strains isolated from 10 animals outside the United States and from three humans within the United States. This group was genetically diverse; five strains were closely related to the type strain of C. cryaerophila (DNA hybridization group 1A), and eight strains were more closely related to one another (DNA hybridization group 1B). Strains in DNA hybridization group 1B were phenotypically diverse, with two of eight strains resembling C. cryaerophila. The seven strains from DNA hybridization groups 1A and 1B which resembled C. cryaerophila and the C. cryaerophila type strain were aerotolerant only at 30 degrees C and catalase positive, did not grow in glycine or on MacConkey agar, were generally susceptible to nalidixic acid, and were resistant to cephalothin. The remaining six strains of DNA hybridization group 1B phenotypically resembled C. butzleri; however, they were generally catalase positive and susceptible to nalidixic acid and cephalothin. DNA hybridization group 1B is not designated as a separate species at this time since it cannot, with certainty, be separated genetically from C. cryaerophila or phenotypically from C. butzleri.  相似文献   
55.
W C Chan  G Ye  S Link  A C Mawle    J K Nicholson 《Immunology》1989,67(1):56-61
The effect of anti-CD2 and Fc receptor binding molecules on the cytolytic function of a highly enriched population of CD3- large granular lymphocytes (LGL) was studied. These cells could mediate natural killer (NK) activity, antibody-dependent cellular cytotoxicity (ADCC) and lectin-dependent cellular cytotoxicity (LDCC). Both ADCC and LDCC were enhanced by anti-CD2. The enhanced LDCC could also be observed with IL-2-activated LGL. However, NK cell activity was usually slightly diminished or unaffected by anti-CD2 binding. Immune complex and aggregated human IgG had no effect on ADCC but an anti-CD16 showed a dose-dependent inhibition of ADCC, reversible by anti-HLA-ABC and anti-CD2. Cross-linking of LGL surface-bound anti-CD2 caused an almost complete inhibition of LDCC and ADCC but had much less effect on NK activity. These experiments show that ADCC and LDCC mediated by CD3- LGL can be influenced by perturbing the CD2 molecule. NK activity was, however, affected differently, suggesting some basic differences in the pathway of ADCC and NK function.  相似文献   
56.
The cause(s) of sarcoidosis is unknown. Mycobacterium spp. are suspected in Europe and Propionibacterium spp. are suspected in Japan. The present international collaboration evaluated the possible etiological links between sarcoidosis and the suspected bacterial species. Formalin-fixed and paraffin-embedded sections of biopsy samples of lymph nodes, one from each of 108 patients with sarcoidosis and 65 patients with tuberculosis, together with 86 control samples, were collected from two institutes in Japan and three institutes in Italy, Germany, and England. Genomes of Propionibacterium acnes, Propionibacterium granulosum, Mycobacterium tuberculosis, Mycobacterium avium subsp. paratuberculosis, and Escherichia coli (as the control) were counted by quantitative real-time PCR. Either P. acnes or P. granulosum was found in all but two of the sarcoid samples. M. avium subsp. paratuberculosis was found in no sarcoid sample. M. tuberculosis was found in 0 to 9% of the sarcoid samples but in 65 to 100% of the tuberculosis samples. In sarcoid lymph nodes, the total numbers of genomes of P. acnes or P. granulosum were far more than those of M. tuberculosis. P. acnes or P. granulosum was found in 0 to 60% of the tuberculosis and control samples, but the total numbers of genomes of P. acnes or P. granulosum in such samples were less than those in sarcoid samples. Propionibacterium spp. are more likely than Mycobacteria spp. to be involved in the etiology of sarcoidosis, not only in Japanese but also in European patients with sarcoidosis.  相似文献   
57.
58.
Kleihauer examination of peripheral blood cannot be used reliably to detect transplacental fetal-maternal haemorrhage in mothers with hereditary persistence of fetal haemoglobin (HPFH). In Rh(D) negative pregnancies diagnostic confusion with a large fetal-maternal haemorrhage could result in the administration of inappropriately excessive amounts of anti-D immunoglobulin, and the inability to diagnose and quantify transplacental haemorrhage in maternal HPFH by current methods could result in insufficient anti-D administration and subsequent Rh(D) sensitisation. Accordingly, a method to detect and quantify fetal-Rh(D) positive maternal haemorrhage using erythrocyte fluorescent immunocytometry was developed. An indirect immunofluorescence method with IgG anti-D immunoglobulin as the primary antibody was used, combined with quantitative analysis on a fluorescence activated cell sorter. The method was accurate, specific, and sensitive and could detect a contaminating population of 0.1% Rh(D) positive cells in Rh(D) negative blood--a level of fetal-maternal haemorrhage well covered by a single dose of 500 IU of anti-D immunoglobulin.  相似文献   
59.
AIMS: To compare the performance of a new chromogenic medium, Uriselect 4, with cystine lactose electrolyte deficient (CLED) agar and an established chromogenic agar, CPS ID 2 medium, for detection of urinary tract pathogens. METHODS: Using a semiquantitative culture method, 777 samples were inoculated on to the three test media in duplicate. All bacterial strains that yielded a potentially significant growth were observed for colony colour and identified using standard methods. RESULTS: Of the 777 samples tested, 589 urine samples yielded potentially significant growth of at least one strain. A total of 811 strains were isolated on at least one of the three media. A total of 168 urine samples yielded a mixture of at least two strains. Uriselect 4 medium showed the best sensitivity of the three media and only failed to recover 14 strains (1.7%). CPS ID 2 medium failed to recover 22 strains (2.7%). CLED medium showed the worst recovery and failed to recover 74 strains (9.1%). Both chromogenic media allowed for identification of Escherichia coli with a high degree of specificity (98% for Uriselect 4, 99.7% for CPS ID 2). Inclusion of a spot indole test increased the specificity of both chromogenic media to 100% for E coli. CONCLUSIONS: Uriselect 4 and CPS ID 2 were superior to CLED medium for the isolation of urinary tract pathogens mainly because of their ability to discriminate mixed cultures. Both chromogenic media were also useful for the preliminary identification of the most common urinary tract pathogens.  相似文献   
60.
Immunoblots were used to study the immunoglobulin G response to Borrelia burgdorferi in experimentally and naturally exposed dogs. Adsorption studies confirmed that the antibodies were specific for B. burgdorferi. Experimentally exposed dogs were asymptomatic. Naturally exposed dogs included both asymptomatic animals and animals showing signs compatible with Lyme disease. Naturally exposed dogs were from four geographic regions of the country. No differences were detected between immunoblot patterns of naturally exposed symptomatic or asymptomatic dogs from different areas of the country. The immunoblot patterns obtained with sera from experimentally exposed dogs were different from those obtained with sera from naturally exposed dogs and were characterized by reactivity to fewer and different protein bands. Immunoblot analysis using an OspA-protein-producing Escherichia coli recombinant showed that experimentally exposed dogs produced antibodies to OspA, whereas naturally exposed dogs did not. Modifications of the immune response over time, different routes of antigen presentation, and strain variation are factors postulated to account for the observed differences.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号